WO2018113268A1 - 锂离子电池及其电解液 - Google Patents

锂离子电池及其电解液 Download PDF

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WO2018113268A1
WO2018113268A1 PCT/CN2017/092318 CN2017092318W WO2018113268A1 WO 2018113268 A1 WO2018113268 A1 WO 2018113268A1 CN 2017092318 W CN2017092318 W CN 2017092318W WO 2018113268 A1 WO2018113268 A1 WO 2018113268A1
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ion battery
lithium ion
formula
compound
electrolyte
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PCT/CN2017/092318
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English (en)
French (fr)
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朱建伟
韩昌隆
周晓崇
郇凤
刘继琼
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宁德时代新能源科技股份有限公司
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention belongs to the field of new energy materials, and more particularly, to a lithium ion battery and an electrolyte solution thereof which have improved heat generation problems and have good storage performance.
  • Lithium-ion batteries have been widely researched and widely used in mobile phones and portable computers in recent years due to their high specific energy, high operating voltage, wide application temperature range, low self-discharge rate, long cycle life, no pollution and good safety performance.
  • mobile electronic devices such as cameras and cameras
  • traditional batteries are gradually being replaced in the fields of aerospace, aerospace, marine, satellite, small medical instruments and military communication equipment.
  • the pursuit of high energy density of lithium-ion batteries has become an irresistible trend.
  • the commonly used ones are to increase the working voltage of the positive electrode material, to use high-nickel materials with high gram capacity, and to use negative electrode materials with higher discharge capacity.
  • the high nickel content of the positive electrode with the increase of nickel content the oxidization of the delithiation state of the material is obviously enhanced, and the electrolyte is easily oxidatively decomposed on the surface of the de-lithium high nickel material, which deteriorates the cycle life of the cell, which is currently The electrolyte presents a great challenge.
  • the silicon material has a theoretical specific capacity much higher than that of the graphite negative electrode material, and there is a huge volume expansion during the cycle.
  • the solid electrolyte interface (SEI) film of the negative electrode is broken during the cycle, resulting in reductive decomposition of the electrolyte.
  • SEI solid electrolyte interface
  • a large amount of by-products are generated, which deteriorates cycle performance.
  • the activity of reacting the positive and negative electrodes with the electrolyte is further enhanced, the heat of reaction is greatly increased, and a large amount of gas is generated, which causes volume expansion of the battery, and may cause battery internalization in severe cases. A short circuit has occurred.
  • the object of the present invention is to overcome the serious problem of high-temperature gas production of the existing lithium ion battery, and to provide a Lithium-ion battery and electrolyte solution with improved high-temperature gas production problems and good storage performance.
  • the present invention provides a lithium ion battery electrolyte comprising a lithium salt, an organic solvent and an additive, the additive comprising a compound of the formula I and a compound of the formula II, the structural formula of which is as follows:
  • R 1 , R 2 and R 3 are independently selected from a halogen atom, a phenyl group, an alkane group having a carbon number of 0 to 9 which is completely or partially substituted by a halogen atom, and is completely substituted by a halogen atom.
  • the compound of the formula I is one or more of propylene 2,2-difluoropropionate, propylene 2-bromoisobutyrate or propylene pivalate.
  • the structural formula of propylene 2,2-difluoropropionate, propylene 2-bromoisobutyrate and propylene pivalate is as follows:
  • the compound of the formula II is fluoroethylene carbonate, 1,2-difluoroethylene carbonate or vinyl chlorocarbonate; fluoroethylene carbonate, 1,
  • the structural formula of 2-difluoroethylene carbonate and chloroethylene carbonate is as follows:
  • the compound of the formula I accounts for 0.01 to 5% of the total mass of the electrolyte of the lithium ion battery.
  • the additive cannot form a dense SEI film on the positive electrode, and the high-temperature storage gas production of the system is not significantly improved; when the content of the compound of the formula I is too high, it may be formed.
  • Excessive thick SEI film significantly increases the interface impedance of the positive electrode surface, and also deteriorates the battery's 25 ° C, 45 ° C cycle performance.
  • the compound of the formula I accounts for 0.1 to 3% of the total mass of the electrolyte of the lithium ion battery.
  • the compound of the formula II accounts for 0.5 to 30% of the total mass of the electrolyte of the lithium ion battery.
  • the content of the compound of the formula II is related to the composition and content of the negative electrode material: when the content of the compound of the formula II in the electrolyte is too low, the active interface of the negative electrode is caused, especially in the case of the silicon-based negative electrode system, the active particles cannot be effectively protected, and then occur.
  • a large number of side reactions such as the generation of a large amount of reducing gas to destroy the interface stability, resulting in worsening of the cycle performance of the cell; conversely, when the content of the compound of formula II in the electrolyte is too high, especially under high temperature conditions, during charging and discharging of the lithium battery,
  • the high-nickel material in the strong oxidation state is oxidatively decomposed by contact with the electrolyte, and the by-product HF generated by the like may cause destruction of the structure of the positive electrode material and deteriorate the cycle performance of the lithium battery.
  • the additive further includes a cyclic ester compound containing a sulfur-oxygen double bond, such as vinyl sulfate. Its function is to further improve the storage performance of the lithium battery, and to some extent improve the cycle performance of the lithium ion battery.
  • the lithium salt is a conventional choice, optionally including, but not limited to, LiPF 6 , LiBF 4 , LiN(SO 2 F) 2 , LiN (CF 3 SO 2 2 ), LiClO 4 , LiAsF 6 , LiB(C 2 O 4 ) 2 , LiBF 2 (C 2 O 4 ), LiN(SO 2 R F ) 2 , LiN(SO 2 F)(SO 2 R F ) One or more, wherein R F is C n' F 2n'+1 and n' is from 1 to 10.
  • the lithium salt accounts for 6.25 to 25% of the total mass of the electrolyte of the lithium ion battery.
  • the organic solvent may be selected according to actual needs, preferably a non-aqueous organic solvent, such as a carbon number of 1-8, and containing at least one ester group. compound of.
  • the organic solvent is ethylene carbonate, propylene carbonate, butylene carbonate, pentene carbonate, fluoroethylene carbonate, dimethyl carbonate, carbonic acid
  • ethyl ester, dipropyl carbonate, and ethyl methyl carbonate may be one or more of halogenated derivatives of the above compounds.
  • the present invention also provides a lithium ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, the electrolyte comprising a lithium salt, an organic solvent and an additive, the additive comprising a compound of the formula I and a compound of the formula II
  • a lithium ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, the electrolyte comprising a lithium salt, an organic solvent and an additive, the additive comprising a compound of the formula I and a compound of the formula II
  • R 1 , R 2 and R 3 are independently selected from a halogen atom, a phenyl group, an alkane group having a carbon number of 0 to 9 which is completely or partially substituted by a halogen atom, and is completely substituted by a halogen atom.
  • the lithium ion battery and the electrolyte thereof of the invention have the following characteristics:
  • the invention provides an electrolyte comprising a compound of the formula I and a compound of the formula II, the compound of the formula II can form a dense and high-tough solid electrolyte interface (SEI) film on the negative electrode, improving the cycle performance of the lithium ion battery, but at the same time, it is easy
  • SEI solid electrolyte interface
  • the gas production problem inside the battery is serious; through the introduction of the compound of formula I, the polymerization reaction can be effectively formed at the positive electrode interface and a dense and uniform SEI film is formed, which effectively isolates the positive electrode material and electrolyte in the high oxidation state during charging and discharging of the lithium battery.
  • the contact solves the serious gas production problem caused by the compound of the formula II and prevents the corrosion damage of the negative electrode by hydrofluoric acid (HF), so that the positive and negative interfaces of the lithium ion battery are stable.
  • HF hydrofluoric acid
  • an electrolyte system containing a compound of formula I and formula II is applied to high energy In the high density nickel/silicon negative electrode lithium ion battery system, the gas production suppression effect is remarkable.
  • the combination of the vinyl sulphate compound and the compound of the formula I and the formula II not only overcomes the serious defects of high-temperature storage gas production of the lithium battery, ensures the stability of the electrode interface of the lithium battery, and ensures that the cycle performance of the lithium ion battery is not affected. Effectively improve the circulating residual capacity of the lithium ion battery, so that the lithium ion battery exhibits good electrochemical performance.
  • Lithium-ion batteries (referred to as batteries) S1 are prepared according to the following methods:
  • Lithium nickel cobalt manganese oxide LiNi 0.8 Co 0.1 Mn 0.1 O 2
  • a binder polyvinylidene fluoride
  • a conductive agent conductive carbon black
  • the silicon-carbon composite, the conductive agent (conductive carbon black), and the binder polyacrylate are mixed at a weight ratio of 98:1:1, and after adding to the deionized water, the negative electrode slurry is obtained under the stirring of a vacuum mixer.
  • the anode slurry was uniformly coated on the copper foil; the copper foil was air-dried at room temperature, transferred to an oven at 120 ° C for 1 hour, and then subjected to cold pressing and slitting to obtain a negative electrode sheet.
  • the EC and DEC which have been subjected to the rectification and dehydration purification treatment are uniformly mixed to form an organic solvent, the sufficiently dried lithium salt is dissolved in the above organic solvent, and then the lithium salt LiPF 6 and the additive are added in an organic solvent of 8 wt%.
  • the fluoroethylene carbonate and 0.5 wt% of propylene trifluoroacetate were uniformly mixed to obtain an electrolytic solution.
  • the concentration of lithium salt is 1 mol / L
  • the content is 12.5% of the total mass of the electrolyte
  • the conventionally-cut positive electrode and negative electrode sheets and lithium battery separator are stacked in order, so that the lithium battery separator acts as a separator between the positive and negative electrodes, and then wound to obtain a bare cell; It is placed in the outer packaging foil, and the prepared electrolyte solution is injected into the dried battery, and subjected to vacuum encapsulation, standing, formation, shaping, and the like to obtain a lithium ion battery (S1 for short).
  • Examples 2 to 19 (S2 to S19) and Comparative Examples 1 to 8 (D1 to D8) were prepared in the same manner as in Example 1, except that the additives in the electrolytic solution, and the types and contents of the specific additives are shown in Table 1.
  • the batteries obtained in Comparative Examples 1 to 8 and Examples 1 to 19 were each subjected to the following tests: respectively, at 25 ° C and 45 ° C, the battery was charged at a constant current of 1 C to 4.2 V, and then charged to a current at a constant voltage. 0.05C, and then use 1C constant current discharge to 2.8V, this time is the first cycle, according to the above conditions, the battery is repeatedly cycled, respectively, to calculate the capacity retention rate after battery cycle 200, 400, 600 times, wherein The capacity retention rate after the cycle is calculated according to the following formula. See Table 2 and Table 3 for the relevant test data.
  • the capacity retention ratio after the cycle (corresponding to the discharge capacity of the cycle / the discharge capacity of the first cycle) ⁇ 100%.
  • the batteries S1 to S19 and the batteries D1 to D8 were respectively subjected to the following tests:
  • Lithium-ion battery is charged to 4.2V at a constant current of 1C at room temperature, then charged at a constant voltage of 4.2V to a current of 0.05C, and the volume of the battery is tested as V 0 ; then the lithium ion battery is placed in an incubator at 80 ° C, and stored 10 Days, and the volume of the test battery was taken out on the nth day and recorded as V n , and the volume expansion ratio of the lithium ion battery on the 10th day was calculated by the following formula. The results are shown in Table 4.
  • the volume expansion ratio (%) of lithium ion battery after high temperature storage for n days (V n - V 0 ) / V 0 ⁇ 100%, where n is the number of days of high-temperature storage of the lithium ion battery.
  • the amount of the negative electrode film forming agent (the compound of the formula II) is related to the negative electrode material composition of the battery design system.
  • the negative electrode material such as the negative active material, silicon and silicon materials are used, and the content of the active material is higher.
  • the amount of film forming additive (compound of formula II) required is also greater.
  • the content of the compound of formula II in the electrolyte is too high, especially under high temperature conditions, during the charging and discharging process of the lithium battery, the high-nickel material of the strong oxidation state is oxidatively decomposed by contact with the electrolyte, and the by-product HF etc.
  • the structure of the positive electrode material is destroyed, and the cycle performance of the lithium battery is also deteriorated.
  • the additive formula I and the compound of formula II are simultaneously added to the electrolyte system, and more and less formula II are in the electrolyte system.
  • the additive can form a stable SEI film, and the gas generation problem can be effectively suppressed by the addition of the compound of the formula I.
  • the lithium battery has the same cycle performance at 25 ° C and 45 ° C, and the gas production problem of the high temperature storage is also effectively suppressed.
  • the use of the additive C (vinyl sulfate) in combination with a compound of the formula I, formula II or the like can further improve electrochemical performance such as cycle performance and capacity storage of the cell.
  • the compound of the formula I of the present invention can be found as a gas generating inhibitor, and the compound of the formula II is used as a film-forming agent in combination with an electrolyte, and the obtained lithium ion battery can ensure the cycle performance at 25 ° C and 45 ° C. On a consistent basis, It can also significantly improve the storage gas production of lithium ion batteries at 80 ° C high temperature.

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Abstract

一种锂离子电池电解液，包括锂盐、有机溶剂和添加剂，添加剂包括式I化合物和式II化合物，其结构式如下所示：其中，n为1～9，R 1、R 2、R 3独立地选自卤原子、苯基、被卤原子完全取代或部分取代的碳原子数为0～9的烷烃基、被卤原子完全取代或部分取代的碳原子数为0～9的环状烷基；R 4、R 5、R 6、R 7中至少有一个选自F、Br或Cl。通过将式I化合物和式II化合物作为添加剂添加到电解液中，可以显著改善锂离子电池的高温产气问题，提高锂离子电池的循环存储性能，具有很好的应用价值。还公开了一种锂离子电池。

Description

锂离子电池及其电解液 技术领域
本发明属于新能源材料领域，更具体地说，本发明涉及一种改善了高温产气问题且存储性能好的锂离子电池及其电解液。
背景技术
锂离子电池因具有比能量高、工作电压高、应用温度范围宽、自放电率低、循环寿命长、无污染和安全性能好等优点，近年来被大量研究并广泛应用于手机、便携式计算机、摄像机、照相机等移动电子设备中，在航空、航天、航海、人造卫星、小型医疗仪器和军用通讯设备领域也逐步代替传统电池。
当今时代，追求锂离子电池高能量密度已经成为大势所趋，目前常用的分别是提高正极材料的工作电压、使用高克容量的高镍材料和使用具有更高放电容量的负极材料。其中，正极高镍材料随着镍含量的增加，材料脱锂态的氧化性明显增强，电解液在脱锂态的高镍材料表面极易发生氧化分解，恶化电芯的循环寿命，这对当前电解液提出了极大的挑战。硅材料具有远高于石墨负极材料的理论比容量，在循环过程中存在巨大的体积膨胀，另外，负极的固体电解质界面(简称SEI)膜在循环过程中发生破裂，导致电解液发生还原分解，生成大量副产物，恶化循环性能。特别是满充电池在高温状态下使用或者存储时，正负极与电解液发生反应的活性进一步增强，反应放热量大幅增加，产生大量气体，导致电池发生体积膨胀，严重时还可能导致电池内发生短路。
有鉴于此，确有必要提供一种改善了高温产气问题且循环存储性能好的锂离子电池及其电解液。
发明内容
本发明的目的在于：克服现有锂离子电池高温产气严重的问题，提供一种 改善了高温产气问题且存储性能好的锂离子电池及其电解液。
为了实现上述发明目的，本发明提供了一种锂离子电池电解液，包括锂盐、有机溶剂和添加剂，所述添加剂包括式I化合物和式II化合物，其结构式如下所示：
Figure PCTCN2017092318-appb-000001
其中，n为1～9，R1、R2、R3独立地选自卤原子、苯基、被卤原子完全取代或部分取代的碳原子数为0～9的烷烃基、被卤原子完全取代或部分取代的碳原子数为0～9的环状烷基；R4、R5、R6、R7中至少有一个选自F、Br或Cl。
作为本发明锂离子电池电解液的一种改进，所述式I化合物为2,2-二氟丙酸丙烯酯、2-溴异丁酸丙烯酯、特戊酸丙烯酯中的一种或几种；2,2-二氟丙酸丙烯酯、2-溴异丁酸丙烯酯、特戊酸丙烯酯的结构式如下：
Figure PCTCN2017092318-appb-000002
作为本发明锂离子电池电解液的一种改进，所述式II化合物为氟代碳酸乙烯酯、1,2-二氟代碳酸乙烯酯或氯代碳酸乙烯酯；氟代碳酸乙烯酯、1,2-二氟代碳酸乙烯酯、氯代碳酸乙烯酯的结构式如下：
Figure PCTCN2017092318-appb-000003
作为本发明锂离子电池电解液的一种改进，所述式I化合物占锂离子电池电解液总质量的0.01～5％。当电解液中的式I化合物的含量过低时，该添加剂无法在正极形成致密的SEI膜，对体系的高温存储产气无明显改善；当式I化合物的含量过高时，则会因为形成过厚的SEI膜而显著增加正极表面的界面阻抗，同时也会恶化电池的25℃、45℃循环性能。
作为本发明锂离子电池电解液的一种改进，所述式I化合物占锂离子电池电解液总质量的0.1～3％。
作为本发明锂离子电池电解液的一种改进，所述式II化合物占锂离子电池电解液总质量的0.5～30％。式II化合物含量与负极材料成分和含量相关：当电解液中的式II化合物含量过低时，会导致负极活性界面，特别是在硅基负极体系时，其活性颗粒无法得到有效保护，进而发生大量的副反应，如产生大量还原性气体破坏界面稳定，导致电芯循环性能加剧恶化；反之，当电解液中式II化合物的含量过高时，尤其在高温条件下，锂电池充放电过程中，强氧化态的高镍材料与电解液接触发生氧化分解反应，产生的副产物HF等会引起正极材料结构的破坏，还会恶化锂电池循环性能。
作为本发明锂离子电池电解液的一种改进，所述添加剂还包括含硫氧双键的环状酯类化合物，如：硫酸乙烯酯等。其作用在于进一步改善锂电池的存储性能，并且一定程度上提高了锂离子电池的循环性能。
作为本发明锂离子电池电解液的的一种改进，所述锂盐为常规选择，可选地，包括但不限于LiPF6、LiBF4、LiN(SO2F)2、LiN(CF3SO2)2、LiClO4、LiAsF6、LiB(C2O4)2、LiBF2(C2O4)、LiN(SO2RF)2、LiN(SO2F)(SO2RF)中的一种或多种，其中，RF为Cn′F2n′+1，n′为1～10。
作为本发明锂离子电池电解液的的一种改进，所述锂盐占锂离子电池电解液总质量的6.25～25％。
作为本发明锂离子电池电解液的的一种改进，所述有机溶剂可以根据实际需求进行选择，优选非水有机溶剂，如碳原子数为1～8、且含有至少一个酯基 的化合物。
作为本发明锂离子电池电解液的的一种改进，所述有机溶剂为碳酸乙烯酯、碳酸丙烯酯、碳酸丁烯酯、碳酸戊烯酯、氟代碳酸乙烯酯、碳酸二甲酯、碳酸二乙酯、碳酸二丙酯、碳酸甲乙酯中的一种或多种，也可以是上述化合物的卤代衍生物中的一种或多种。
为了实现上述发明目的，本发明还提供了一种锂离子电池，包括正极、负极、隔离膜和电解液，所述电解液包括锂盐、有机溶剂和添加剂，添加剂包括式I化合物和式II化合物，其结构式如下所示：
Figure PCTCN2017092318-appb-000004
其中，n为1～9，R1、R2、R3独立地选自卤原子、苯基、被卤原子完全取代或部分取代的碳原子数为0～9的烷烃基、被卤原子完全取代或部分取代的碳原子数为0～9的环状烷基；R4、R5、R6、R7中至少有一个选自F、Br或Cl。
与现有技术相比，本发明锂离子电池及其电解液具有如下特点：
本发明提供的包含式I化合物和式II化合物的电解液，式II化合物可以在负极形成致密且高韧的固体电解质界面(SEI)膜，改善锂离子电池循环性能，但是与此同时，也容易导致电池内部的产气问题严重；通过式I化合物的引入，能够有效在正极界面发生聚合反应并形成致密均匀的SEI膜，有效的隔绝在锂电池充放电过程中高氧化态的正极材料与电解液的接触，解决了式II化合物带来的严重产气问题并阻止氢氟酸(HF)对负极的腐蚀破坏，使得锂离子电池的正负极界面稳定。特别地，将含有式I及式II化合物的电解液体系应用于高能 量密度的高镍/硅负极锂离子电池体系中，其产气抑制效果显著。此外，将硫酸乙烯酯类化合物与式I、式II化合物的配合使用，不仅克服了锂电池高温存储产气严重的缺陷，保证锂电池电极界面稳定，还保证锂离子电池的循环性能不受影响，有效提高锂离子电池的循环剩余容量，使锂离子电池表现出良好的电化学性能。
具体实施方式
为了使本发明的发明目的、技术方案和有益技术效果更加清晰，以下结合实施例，对本发明进行进一步详细说明。应当理解的是，本说明书中描述的实施例仅仅是为了解释本发明，并非为了限定本发明，实施例的配方、比例等可因地制宜做出选择而对结果并无实质性影响。
实施例1
锂离子电池(简称电池)S1均按照下述方法进行制备得到：
(1)正极片的制备
将镍钴锰酸锂(LiNi0.8Co0.1Mn0.1O2)、粘结剂(聚偏氟乙烯)、导电剂(导电碳黑)按照重量比为98:1:1进行混合，加入N-甲基吡咯烷酮(NMP)，在真空搅拌机作用下搅拌至体系成均一透明状，获得正极浆料；将正极浆料均匀涂覆于厚度为12μm的铝箔上；将铝箔在室温晾干后转移至120℃烘箱干燥1h，然后经过冷压、分切得到正极片。
(2)负极片的制备
将硅-碳复合物、导电剂(导电碳黑)、粘结剂聚丙烯酸酯按照重量比为98:1:1进行混合，加入到去离子水后，在真空搅拌机的搅拌作用下获得负极浆料；将负极浆料均匀涂覆在铜箔上；将铜箔在室温晾干后转移至120℃烘箱干燥1h，然后经过冷压、分切得到负极片。
(3)电解液的制备
在干燥房中，将已经精馏脱水纯化处理的EC和DEC混合均匀形成有机溶剂，将充分干燥的锂盐溶解于上述有机溶剂中，然后在有机溶剂中加入锂盐 LiPF6、添加剂为8wt％的氟代碳酸乙烯酯和0.5wt％的三氟乙酸丙烯酯，混合均匀，获得电解液。其中，锂盐的浓度为1mol/L，含量为电解液总质量的12.5％，EC、EMC、DEC的重量比为EC:EMC:DEC＝1:1:1。
(4)锂离子电池的制备
将常规分切的正极片和负极片、锂电池隔离膜按顺序叠好，使锂电池隔离膜处于正、负极片之间起到隔离的作用，然后卷绕得到裸电芯；将裸电芯置于外包装箔中，将上述制备好的电解液注入到干燥后的电池中，经过真空封装、静置、化成、整形等工序，获得锂离子电池(简称S1)。
实施例2～19(S2～S19)以及对比例1～8(D1～D8)，制备方法同实施例1，不同之处在于其电解液中的添加剂，详细添加剂种类及含量参见表1。
表1对比例1～8和实施例1～19中电解液添加剂的种类和用量
Figure PCTCN2017092318-appb-000005
Figure PCTCN2017092318-appb-000006
注：表1中“-”表示不添加任何物质。
性能测试
锂离子电池25℃以及45℃的循环测试
将对比例1～8和实施例1～19得到的电池均分别进行下述测试：分别在25℃以及45℃下，将电池，以1C恒流充电至4.2V，然后恒压充电至电流为0.05C，再用1C恒流放电至2.8V，此时为首次循环，按照上述条件电池进行多次循环，分别计算得出电池循环200次、400次、600次后的容量保持率，其中，循环后的容量保持率按照下式进行计算，相关测试数据参见表2及表3。
循环后的容量保持率＝(对应循环的放电容量/首次循环的放电容量)×100％。
表2对比例1～8和实施例1～19所得电池在25℃下的循环容量保持率
Figure PCTCN2017092318-appb-000007
Figure PCTCN2017092318-appb-000008
表3对比例1～8和实施例1～19所得电池在45℃下的循环容量保持率
Figure PCTCN2017092318-appb-000009
Figure PCTCN2017092318-appb-000010
锂离子电池在80℃的存储测试
将电池S1～S19以及电池D1～D8分别进行下述测试：
将锂离子电池在室温下以1C恒流充电至4.2V，然后恒压4.2V充电至电流为0.05C，测试电池的体积V0；之后将锂离子电池放入80℃的恒温箱，储存10天，且第n天取出测试电池的体积并记为Vn，通过下式分别计算得出锂离子电池在第10天的体积膨胀率，结果请参见表4。
锂离子电池高温存储n天后的体积膨胀率(％)＝(Vn-V0)/V0×100％，其中n 为锂离子电池高温存储的天数。
表4对比例1～8和实施例1～19得到的电池80℃存储体积膨胀率
Figure PCTCN2017092318-appb-000011
从表2及表3可以得知，与仅添加式II化合物的电池D2～D3相比，同时 加入式I和式II添加剂的电池S1～S5、S8～S19在25、45℃循环下电池的容量保持率基本一致；但是与D5～D8仅添加式I化合物的电池相比，其25、45℃循环的容量保持率明显较高。这表明，在足够量的式II化合物作为硅负极成膜添加剂，合理量的式I化合物的引入，对锂电池的25℃、45℃的循环性能影响不会很大。
从表4可以看出，同时加入式I和式II化合物作为电解液添加剂的S1～S19电池在高温存储后，均具有较低的体积膨胀率。由S1～S5、S8与S19可以看出，式I化合物(包括混合使用)与式II化合物联用，可以很好的解决成膜添加剂(式II化合物)带来的严重产气问题。随着式I化合物含量的增加，电池高温的产气得到有效抑制；当式I化合物含量达到5％时，产气抑制作用趋于平缓。但是，当式I的添加量过高时(S6,6wt％)，在负极会形成过厚的SEI膜，增加电池的DCR，恶化常温及高温循环，极大降低电池的电化学性能。
负极成膜剂(式II化合物)的使用量与电池设计体系的负极材料成分相关，对于高能量密度设计的电池，如负极活性物质选用硅及硅类材料，其活性物质的含量越高，所需的成膜添加剂(式II化合物)量也越多。当电解液中的式II化合物含量过高时，尤其在高温条件下，锂电池充放电过程中，强氧化态的高镍材料与电解液接触发生氧化分解反应，产生的副产物HF等会对导致正极材料结构破坏，也会恶化锂电池循环性能。而在本发明电解液体系中，由S3、S8、S9以及S14～S19可以发现，在电解液体系中同时加入添加剂式I和式II化合物，在电解液体系中较多与较少的式II添加剂，都能形成稳定的SEI膜，并且产气问题能够通过式I化合物的加入得到有效抑制，锂电池的25℃、45℃循环性能都表现一样，高温存储的产气问题也得到有效抑制。
此外，添加剂C(硫酸乙烯酯)与式I、式II等化合物联合使用能够进一步改善电芯的循环性能和容量存储等电化学性能。综合以上，可以发现本发明式I化合物作为产气抑制剂，式II化合物作为成膜剂，联合应用于电解液中，制得的锂离子电池在保证25℃、45℃下的循环性能与原有水平一致的基础上， 还可显著改善锂离子电池在80℃高温下的存储产气问题。
根据上述说明书的揭示和教导，本发明所属领域的技术人员还可以对上述实施方式进行适当的变更和修改。因此，本发明并不局限于上面揭示和描述的具体实施方式，对本发明的一些修改和变更也应当落入本发明的权利要求的保护范围内。此外，尽管本说明书中使用了一些特定的术语，但这些术语只是为了方便说明，并不对本发明构成任何限制。

Claims (10)

  1. 一种锂离子电池电解液，包括锂盐、有机溶剂和添加剂，其特征在于，所述添加剂包括式I化合物和式II化合物，其结构式如下所示：
    Figure PCTCN2017092318-appb-100001
    其中，n为1～9，R1、R2、R3独立地选自卤原子、苯基、被卤原子完全取代或部分取代的碳原子数为0～9的烷烃基、被卤原子完全取代或部分取代的碳原子数为0～9的环状烷基；R4、R5、R6、R7中至少有一个选自F、Br或Cl。
  2. 根据权利要求1所述的锂离子电池电解液，其特征在于，所述式I化合物为：
    Figure PCTCN2017092318-appb-100002
    中的一种或几种。
  3. 根据权利要求1所述的锂离子电池电解液，其特征在于，所述式II化合物为：
    Figure PCTCN2017092318-appb-100003
  4. 根据权利要求1所述的锂离子电池电解液，其特征在于，所述式I化合 物占锂离子电池电解液总质量的0.01～5％。
  5. 根据权利要求4所述的锂离子电池电解液，其特征在于，所述式I化合物占锂离子电池电解液总质量的0.1～3％。
  6. 根据权利要求1所述的锂离子电池电解液，其特征在于，所述式II化合物占锂离子电池电解液总质量的0.5～30％。
  7. 根据权利要求1所述的锂离子电池电解液，其特征在于，所述添加剂还包括含硫氧双键的环状酯类化合物。
  8. 根据权利要求1所述的锂离子电池电解液，其特征在于，所述锂盐为LiPF6、LiBF4、LiN(SO2F)2、LiN(CF3SO2)2、LiClO4、LiAsF6、LiB(C2O4)2、LiBF2(C2O4)、LiN(SO2RF)2、LiN(SO2F)(SO2RF)中的一种或多种，其中，RF为Cn′F2n′+1，n′为1～10。
  9. 根据权利要求1所述的锂离子电池电解液，其特征在于，所述有机溶剂为非水有机溶剂。
  10. 一种锂离子电池，包括正极、负极、隔离膜和电解液，其特征在于，所述电解液为权利要求1～9中任意一项所述的锂离子电池电解液。
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